Chemical sensors are generally known for use in a wide variety of areas such as medicine, scientific research, industrial applications and the like. Fiber optic and electrochemical approaches are generally known for use in situations where it is desired to detect and/or measure the concentration of a parameter at a remote location without requiring electrical communication with the remote location. Structures, properties, functions and operational details of fiber optic chemical sensors can be found in U.S. Pat. No. 4,577,109 to Hirschfeld, U.S. Pat. No. 4,785,814 to Kane, and U.S. Pat. No. 4,842,783 to Blaylock, as well as Seitz, "Chemical Sensors Based on Fiber Optics," Analytical Chemistry, Vol. 56, No. 1, January 1984, each of which is incorporated by reference herein.
Publications such as these generally illustrate that it is known to incorporate a chemical sensor into a fiber optic waveguide, an electrochemical gas sensor or the like, in a manner such that the chemical sensor will interact with the analyte. This interaction results in a change in optical properties, which change is probed and detected through the fiber optic waveguide or the like. These optical properties of chemical sensor compositions typically involve changes in colors or in color intensities. In these types of systems, it is possible to detect particularly minute changes in the parameter or parameters being monitored in order to thereby provide especially sensitive remote monitoring capabilities. Chemical sensor compositions that are incorporated at the distal end of fiber optic sensors are often configured as membranes that are secured at the distal tip end of the waveguide device or optrode.
Sensors of this general type are useful in monitoring the pH of a fluid, measuring gas concentrations such as oxygen and carbon dioxide, and the like. Ion concentrations can also be detected, such as potassium, sodium, calcium and metal ions.
A typical fiber optic pH sensor positions the sensor material at a generally distal location with the assistance of various different support means. Support means must be such as to permit interaction between the pH indicator and the substance being subjected to monitoring, measurement and/or detection. With certain arrangements, it is desirable to incorporate membrane components into these types of devices. Such membrane components must possess certain properties in order to be particularly advantageous. Many membrane materials have some advantageous properties but also have shortcomings. Generally speaking, the materials must be biocompatible, hemocompatible for use in the bloodstream and selectively permeable to hydrogen ions.
It is also desirable to have these membrane materials be photocurable (such that curing is easier, can be done more rapidly, on a smaller scale, and directly on the optical fiber) and resistant to shear forces (e.g., as present in a bloodstream. It is also preferred, clearly, that a signal of sufficient intensity be produced, such that measurement is as accurate as is reasonably possible. It is additionally desired that the materials used for the sensor membrane be constructed such that pH values in a physiologic blood range may be accurately measured, and that the response time for measuring pH values is relatively rapid. An additional desirable property of a sensor for monitoring pH in blood or other physiologic fluid is that the sensor has minimal sensitivity to interfering substances. The optical pH sensors that are currently available are frequently inadequate with regard to one or more of the aforementioned criteria.
The present invention is addressed to a novel fluorescent polymer composition that is particularly suitable for use as a membrane and a membrane-like component in an optical pH sensor and which provides for optical sensors which meet each of the above-mentioned criteria. That is, optical sensors as provided herein provide for good signal intensity, are rapidly cured with light, and are resistant to shear forces such as those present in flowing blood. In addition, pH sensors prepared using the novel polymer compositions have enhanced barrier properties such that the sensor is minimally sensitive to contaminating substances.